1. Field of the Invention
The present invention relates to a switching device for detecting a voltage interruption at a control unit in a motor vehicle with a nonvolatile memory for storage of calibration data for an actuator that can be adjusted by the control unit and a drive unit. The invention further relates to a method for automatic recalibration of a control unit for a drive unit of an actuator following an interruption of an external voltage supply wherein the actuator is moved by the drive unit to a defined position for calibration and wherein the calibration data are subsequently adjusted using the actual position detected and are stored in a nonvolatile memory.
2. Description of the Background Art
Electric motor drive units are increasingly used for moving actuators in motor vehicles. The drive units here are controlled or regulated through signal processing arrangements. DE 38 29 405 A1 illustrates a signal processing arrangement that detects discrete signals of a rotation sensor located in the electric motor. Each of the signals corresponds to a small constant travel of an actuator that is driven by the drive unit. The actual position of the actuator is determined from these sensor signals in conjunction with a direction of rotation of the electric motor. In this context, the drive unit and the signal processing arrangement are typically connected to an electrical system of the motor vehicle through a common power supply line. However, if the voltage supply to the electrical system is interrupted, data stored in the drive unit or signal processing arrangement are lost. As a result, actual positions of the actuators are no longer known once the voltage supply is restored. Thus, position regulation or control by the signal processing arrangement is no longer possible at first.
So that the actual positions of the actuators are not lost, DE 197 26 752 A1 discloses a method for operating an electric motor drive unit in which interruptions of the supply voltage are detected and appropriate measures are initiated to keep the actual positions from being lost. This patent document describes a method for operating an electric motor drive unit that is integrated in at least one circuit with a signal processing arrangement for controlling or regulating the electric motor and with a switch through which the interruptions or contact disruptions of the circuit are detected and communicated to the signal processing arrangement, whereby interruptions or contact disruptions are detected by sensing the current flowing in the circuit. In the event that an interruption in the supply voltage is detected, the actual position of the actuator is determined by analyzing the rotation signals of the electric motor's armature shaft. To this end, two Hall sensors are installed at the end of the motor armature shaft, and emit a signal that is appropriately proportional to the rotation of the motor armature shaft. The Hall sensor signals are incremented or decremented as a function of the direction of rotation in another nonvolatile memory of the signal processing arrangement. A summation of the increments or decrements represents an absolute actual position of the actuator. Thus, the signal processing arrangement can then be without a voltage supply, for example, when the vehicle battery or the drive unit is replaced in the event of maintenance work on the motor vehicle.